Apparatus for fractionating finely divided material



P. S. ROLLER Nov. 5, 1935.

APPARATUS FOR FRACTIONATING FINELY DIVIDED MATERIAL Filed Oct. 26. 1929 FIG. 2

FIG.

WJKINVENTOR Patented Nov. 5, 1935 UNITE STTES arrmarvsbron FRACTIONATING FINELY IVIDED MATE RIAL 7 Claims.

This invention relates to a method and means of separating or fractionating finely divided or powdered material and provides improvements therein.

It provides an improved fractionating means and method whereby very well defined fractions, as regards particle size, may be separated. It provides a method and means whereby well-defined fractions of smaller size particles than heretofore carried out, at least in an effective, simple and relatively expeditious manner, may be effected.

It further provides a method and means of quantitatively analyzing powdered material, and obtaining very accurate results in a relatively simple and expeditious manner.

Air (or any appropriate fluid) is used in the presentmethod and means, and fractions from 0-5 microns are readily separated, and the range may be even smaller.

In the case of analysis of a microscopic particle size powder the fractionations are based on Stokes law which relates the terminal velocity of fall of a spherical particle to its diameter.

The failure of the numerous attempts previously made to separate the finest fractions of a microscopic powder is chiefly due to the impossibility of overcoming the tendency of the minukst particles to cohere strongly, .both to themselves and to the larger grains.

In the design of asuitable apparatus it must be considered that a particle finds itself in a field of force from which it mus be separated by a sufiicient momentum. Since the momentum of the inlet blast is constant in direction, it is necessary to circulate the powder so as to expose fresh portions to the action of the inlet air. Furthermore,

as the initial momentum required is far greater 7 than corresponds to the velocity of fall of the particle, it is necessary to avoid directing the inlet' blast in such a way that the particle is carried by the initial momentum clear up and out of the tube. This condition-is attained. by having the blast impinge into or under the surface of the powder in a direction nearly perpendicular to the vertical.

An embodiment of an apparatus (illustrating also a mode of procedure in carrying out the process) is shown in the accompanying drawin the description which follows being particularly directed to the embodiment of .the invention as an analyzer, though the principle is the same for separation of the material intofractions for utilization, as the purpose for whichthe invention is used.

Referring to said drawing:

Fig. 1 is a front view of the assembled apparatus.

Fig. 2 is a side view of that part'of the apparatus which is used for automatically tapping 5 the powder receptacle.

Fig. 3 is an enlarged diagrammatic view illustrating the position of the powder charge in the receptacle during operation in the absence of the air flow and illustrating the circulation in 10 the mass of the material.

Referring to said drawing, numeral l0 designates a size selecting or separating chamber hereafter conveniently called a settling chamber or cylinder, supported in vertical position in any 15 suitable manner. The settling chamber is preferably made separable from the remainder of the apparatus, so that settling chambers of different diameters may be substituted for the separation of powder fractions or groups of fractions where 20 the particle sizes differ considerably. The length of the settling chamber is so chosen that turbulence in the rising column of air at or near the upper end is eliminated or very nearly so. In, an apparatus for analytical purposes with the 25 gas introduced as hereinafter described this height can remain at approximately 2 feet.

The settling chamber I0 is electrically grounded as indicated at I 2, I 2* to eliminate or reduce adherence of the particles to the walls thereof.

The fluid stream carrying the separated fraction of particles may leave the settling chamber through a goose-neck I4, and a dust collector conveniently in the form of a filter sack or thimble, which serves to collect the particles of the separated fraction, the fluid passing off through the filter.

A container 20 is provided for the powder charge to be separated or fractionated. The container 20 is preferably connected to the bottom 40 or lower-endof the settling chamber by a flexible connection 22, in the form of a rubber tube for example. The flexible connection 22 en-' ables the parts to be relatively moved axially. Ajet of air or other suitable fluid is directed 4 against the powder in the container through a nozzle 25. The nozzle is replaceableby others of diilerent size. The particle-charged gas stream is preferably vbaiiledbe'fore entering the settling chamber. This may be accomplished by direct- 50' ing the jet from the nozzle so that itis more or .less perpendicular to the axis of the settling chamber Ill, whereby it ricochets in the passage leading into the lower end of the separator, and thereby loses force. 7 r

Furthermore the jet from nozzle 25 is preferably so directed as to sweep across or under the surface at a small angle, and thereby more readily lift the particles from the mass, and also produce less compacting effect on the mass.

Means are also preferably provided for circulating the particles in the mass, whereby the different particles are brought to the surface and thereby all of said particles are brought under the effect of the jet directed from nozzle 25. This circulation may be and preferably is produced by a hammer 30 delivering a succession of shakes or taps against the container 20. A rate of 450 taps per minute gives good results in an analytical apparatus. The direction of impact is preferably generally in line with the surface of the mass of powder.

The container furthermore preferably has a concave or hollowed bottom so as to facilitate movement of particles from the bottom of the mass to the surface.

The preferred form of the container 20 is a U-tube having one end connected to the settling chamber I 0 and the other containing the nozzle 25. This form of container incorporates the several advantages hereinbefore pointed out.

The position which the mass of powder assumes in the U-tube'container, in the absence of air flow and the circulation of the particles in the mass is shown in Fig. 3.

An abutment 32 may be provided for imparting an impact to said container 20 on its re-.

bound from the impact of hammer 30, and a spring 34 or other suitable means may be provided for controlling the swing of the container. The combination of the spring and abutment constrains the oscillation of the U-shaped receptacle for producing the effect desired.

The hammer 30 may be actuated in any suitable manner. As here shown it is mounted on a spring-pressed arm 36. A motor driven cam 38 cocks the hammer against the spring and releases it to strike under the reflex of the spring pressed arm, The powder may be introduced through any of the openings leading to the U- tube as preferred. In the embodiment of the invention as an analyzer the powder is introduced preferably through the opening 24 prior to putting nozzle.25 in place.

The operation of the apparatus directed towards its use as an analyser of hue powders is virtually the same for each particle size separation. The only changes are in the rate of air flow, the change in nozzle size and adjustment into position of the inlet tube, and the change in size of the settling chamber.

The apparatus is tested for leaks and the tension on the springs of the automatic hammer adjusted so that a moderate impact is secured. Toward the end of the 0-5 micron separation, the action of the hammer and back-stop causes "the powder to markedly incline downwards from left to right, and indeed the steepness of the slope can be altered by adjusting the strengthof the container 20 up to about the top of the bend, at the center in the case of an analyser is required. This powder is preferably dried for about an hour at 120 C. The air flow is adjust- ,edto the desired rate. The separations may be for example 0-5 microns, 5-10 microns, 10-20- microns, the residuebeingabove60microns.

microns, 20-40 microns, and 40-60 point rate. To determine the rate the powder is 5 collected for a given period of time in the paper thimble, and the latter removed after rapping the tube for a few minutes, at the end of and during which rapping the flow is stopped. The powder is tapped out of the thimble into a watch 0 crystal and weighed. It is important to rap the tube a few minutes before and during the shutting ofi of the air blast in order to shake off any powder adhering to the wall that properly belongs to the fraction separated. The total weight 15 of powder blown over, carefully collected and weighed, is the weight of each fraction. It is desirable to weight the residue left in the U-con- 'tainer at the end of each fractionation as a check for leaks and errors in handling. 20 The invention may receive other embodiments and be carried out by other modes of procedure than those herein specifically illustrated and described.

t is cl imed is:-

I. In an apparatus. for air-separating powders according to particle size a substantially U- shaped container having an inlet and an outlet, means for producing constrained oscillations of said container, means for supplying a jet of air 30 at the inlet of said container, a settling chamber in communication with the outlet of said container, and means for removing particles from the burdened air passing through said container.

2. An apparatus for maintaining effective con- 36 tact between a powder and a fluid jet comprising a substantially U-shaped receptacle, means for producing oscillations of said receptacle, means for modifying each oscillation, an inlet for the fluid, an inlet for the powder, and an out- (a let for the burdened fluid.

3. In combination, a substantially U-shaped container for holding a powder charge, means for producing oscillations of said container, means for constraining each oscillation, an inlet for introducing the powder, an inlet fora fluid jet, an outlet for the burdened fluid, a settling chamber, and means for removing the solids from the-burdened fluid.

4. In an apparatus for the separation of powders, a substantially U-shaped container having an inlet and outlet, means for producing constrained oscillations of said container, means for supplying a jet of fluid at the inlet of said container, a settling chamber in communication with theoutlet of 'said container, and means for removing particles from the burdened fluid passing through said container.

5. In combination, a substantially U-shaped container for holding a powder charge, means for producing oscillations of said container, a spring and abutment for constraining the oscillation, an inlet for introducing the powder, an inlet for a fluid jet, an outlet for the burdened fluid, a settlingchamber, and means for removing the solids from the burdened fluid. I,

6. An apparatus for maintaining 'eifective con-v tact between a powder and a fluid jet comprisa concav t m nt i s' n inlet for flui'dand forpowder and outlet for the burdened fluid, said inlet and outlet separately, arrangedin the upper. portion of the receptacle and at opposite ends of the concave botceptacle, and means for modifying each oscillation.

'7. In an apparatus for the separation of powders, a-concave bottomed container having an inlet and an outlet separately mounted in the upper portion of the container and disposed at opposite ends of the concave bottom, means for producing oscillations of said container, means for supplying a jet of fluid at the inlet of said container, a settling chamber in communication with the outlet of said container, and means for removing particles from the burdened fluid passing through 5 said container.

PAUL S. BOILER. 

